1. Field of the Invention
The present invention relates to a method and an apparatus for etching or forming a thin film using plasma in a process of producing a semiconductor device.
2. Description of the Related Art
FIG. 1 shows an example of this sort of conventional apparatus for plasma treatment. A specimen supporting base 3 is provided in a treatment chamber 2 which is formed in a container 1. A pair of electrodes 5a and 5b are disposed outside the container 1 with the container held therebetween, a high frequency power source 6 being connected to the two electrodes 5a and 5b. Gas inlet ports 7 for introducing a reactive gas into the container 1 are formed at one end of the container 1 and a gas outlet port 8 for exhausting a reactive gas is formed at the other end.
Description will now be made of the operation of the apparatus shown in FIG. 1. Specimens 4 such as semiconductor wafers are first set on the specimen supporting base 3. A reactive gas is then introduced into the container 1 through the gas inlet ports 7, as well as being expelled through the gas outlet port 8, and the treatment chamber 2 is thus filled with the reactive gas at a predetermined pressure. In this state, a high frequency voltage is applied between the electrodes 5a and 5b from the high frequency power source 6 to generate plasma in the treatment chamber 2.
At the same time, ions, electrons, activated neutral molecules and neutral atoms and the like are produced in the treatment chamber 2. These particles are subjected to physico-chemical reactions on the surfaces of the specimens 4 which are held on the specimen supporting base 3, etching or formation of a thin film thereby being performed.
The type of reactive gas used and the level of the high frequency voltage applied between the electrodes 5a and 5b will differ according to whether etching or thin film formation is to be conducted.
Since the specimens 4 are gradually electrified to a negative polarity by virtue of the injection of electrons in the plasma produced, however, some of the positive ions in the plasma are accelerated toward the specimens 4 and thus strike the surface of each of the specimens 4. Damage such as crystal defects therefore occurs on the etching surfaces of the specimens 4 during etching or in the thin film formed thereon during thin film formation. The apparatus shown in FIG. 1 thus involves a problem with respect to deterioration in the electrical characteristics of semiconductor devices which are produced using the specimens 4.